Sound Level Surveys and Alarm Audibility Testing
An alarm that cannot be heard is not a warning. It is easy to assume, from a drawing full of neatly spaced sounders, that a building is well covered — but real rooms have furniture, closed doors, soft finishes and background noise, and sound does not always go where the plan said it would. A sound level survey settles the question by measuring what can actually be heard. This guide covers what a survey involves, why audibility must be confirmed rather than assumed, and what to check.
The central point is that audibility should be confirmed by measurement, because how sound really travels in a building can differ from what the design predicted.
Who this is for
This is for competent fire alarm engineers confirming and maintaining alarm audibility. The experience level assumed is competent engineer. Use it for the principles; how and where measurements are taken follows BS 5839-1 and good practice, using suitably calibrated equipment. The aim is evidence that the warning reaches where it must, not an assumption drawn from the layout.
What a survey measures
A sound level survey measures the audibility of the alarm around a building using a sound level meter, to confirm the warning can be heard where it needs to be rather than assuming coverage from a drawing. Audibility requirements are addressed in BS 5839-1, and a survey provides evidence that they are met in practice. It turns coverage from a claim into a measured result. How and where measurements are taken follows BS 5839-1 and good practice, using suitably calibrated equipment, so the result reflects real coverage. The survey's value is precisely that it deals in what is heard, not what was intended.
Why measure, not assume
The reason a survey matters is that the building itself shapes the sound. The real building — its finishes, furniture, doors, background noise and any changes since installation — affects how sound actually travels, so measured audibility can differ from what a design predicted. A survey checks reality rather than intention, and from field experience the difference is often real: an area that looks covered on paper can be marginal or inaudible once doors are shut and machinery is running. This matters because a warning that cannot be heard in part of a building is a genuine gap in life safety. Confirming audibility by measurement, against the requirements of BS 5839-1, replaces assumption with evidence.
When a survey is useful
A survey earns its place at particular moments. It is useful at commissioning to confirm coverage from the outset, and after changes — new partitions, altered use, added background noise, or reported inaudibility — that could affect how the alarm is heard. It is also valuable wherever there is genuine doubt about coverage in specific areas. When a survey is appropriate follows the situation and good practice, within BS 5839-1. The common thread is confirming, by measurement, that the warning still reaches where it must after anything that could have changed it — because change is exactly what quietly erodes audibility over a building's life.
Acting on the results
A survey is only worth doing if its findings are acted on. Confirm the alarm is audible where required, identify any areas that fall short, and check that changes to the building or its use have not created inaudible areas since the last check. From field experience, areas of poor audibility — behind heavy doors, in noisy plant spaces, in rooms altered after installation — and changes that have degraded coverage are the findings that matter most. Record the measured results, and flag any area where the warning cannot be adequately heard so coverage can be improved, rather than leaving a known-inaudible area to be discovered in an emergency.
Common points to check
Recurring issues include areas of poor audibility, coverage degraded by building or use changes, and audibility assumed from the design rather than measured. Confirming, by measurement, that the warning is heard where required is the essential check.
When not to rely on this alone
When not to use this article: do not treat it as a survey method for a specific building. How a survey is carried out follows BS 5839-1 and good practice, using calibrated equipment, applied by competent professionals.
Relevant standards
Audibility and its measurement sit within BS 5839-1, a code of practice, using suitably calibrated equipment. The legal duty for fire precautions in most non-domestic premises sits under the Regulatory Reform (Fire Safety) Order 2005, with Building Regulations statutory guidance in Approved Document B applying to building work. Separate the legal duty from the recommended methods, and always work to current editions.
Professional disclaimer
This is an educational and workflow resource for competent engineers and does not replace the current British Standards or competent judgement. Verify audibility against current documentation and by measurement with calibrated equipment.
Related documentation
Use this with the current BS 5839-1. Record measured audibility results, and flag any area where the warning cannot be adequately heard after commissioning or any relevant change.